1. Field of the Invention
The present invention relates to an evaporative fuel processing device including a canister for adsorbing an evaporative fuel generated in a fuel tank of a vehicle.
2. Description of the Prior Art
FIG. 5 illustrates a prior art evaporative fuel processing device, in which a first charge passage 01, a second charge passage 02 and a purge passage 03 are connected to one of end faces of a canister in which an adsorbent is accommodated. An atmosphere-opened passage 04 is defined in the other end face. The first charge passage 01 is connected to an upper space in a fuel tank T through a two-way valve 05, and the second charge passage 02 is connected to a breather tube of the fuel tank T through a fuel supply valve 06. Further, the purge passage 03 is connected to an intake passage of an internal combustion engine through a purge valve 07 which is controlled for opening and closing by an electronic control unit U.
With such a prior art evaporative fuel processing device, an evaporative fuel generated during parking or traveling of a vehicle is charged to the canister C through the first charge passage 01, and an evaporative fuel generated during refueling into the vehicle is charged to the canister C through the second charge passage 02. The evaporative fuel charged to the canister C is purged into the intake passage 08 through the purge passage 03.
FIG. 6 illustrates another prior art evaporative fuel processing device, in which a first canister Ca is interposed between a first charge passage 01 and a first purge passage 03a, and a second canister Cb is interposed between a second charge passage 02 and a second purge passage 03b. Purge valves 07a and 07b are provided in the first and second purge passage 03a and 03b, respectively and are controlled for opening and closing by an electronic control unit U.
With this evaporative fuel processing device, an evaporative fuel generated during parking and traveling of a vehicle is charged to the first canister Ca through the first charge passage 01, and an evaporative fuel generated during refueling into a vehicle is charged to the second canister Cb through the second charge passage 02. The evaporative fuels charged to the first and second canisters Ca and Cb are purged into the intake passage 08 through the first and second purge passages 03a and 03b.
In the evaporative fuel processing device shown in FIG. 5, the evaporative fuel generated in the fuel tank T during refueling is supplied to the canister C through the second charge passage 02 to charge the canister C at a high concentration (see FIG. 7A). Thereafter, when the vehicle travels, the purge passage 03 is evacuated into a negative pressure, causing air to be introduced through the atmosphere-opened passage 04 into the canister C, thereby purging the canister C. In this case, when the time of traveling of the vehicle is long, the purging of the canister is completely performed, but when the time of traveling of the vehicle is short, only a left half of the canister C near the atmosphere-opened passage 04 is purged and hence, the concentration of fuel adsorbed in the left half is reduced into a lower level, but the concentration of fuel adsorbed in the right half is maintained at a higher level (see FIG. 7B).
When the vehicle is parked to discontinue the purging, the adsorbed fuel of the higher concentration in the right half of the canister C is diffused into the left half, so that the concentration of the adsorbed fuel in the entire canister C is brought into a medium level (see FIG. 7C). Thereafter, when the evaporative fuel is supplied through the first charge passage 01 to the canister C due to an increase in temperature in the fuel tank T, there is caused a problem that the evaporative fuel supplied cannot completely be adsorbed to the canister C which has already been charged at the medium concentration, and such evaporative fuel may be released through the atmosphere-opened passage 04 to the atmosphere. (see FIG. 7D).
In the evaporative fuel processing device shown in FIG. 6, the two first and second canisters Ca and Cb are required, resulting not only in a complicated structure, but also in a problem that the first canister Ca does not at all contribute to the adsorption of the evaporative fuel generated in a large amount during refueling. Therefore, it is necessary to insure a large capacity for the second canister Cb and thus, the entire canister must be enlarged.